let arr=['长沙','株洲','湘潭','岳阳','常德','衡阳','郴州','永州']
for(var i=0;i<arr.length;i++){
    console.log(arr[i]);
}
for(var i in arr){
    console.log(arr[i]);
}
for(var i of arr){
    console.log(i);
}